Environmental activists filed suit Tuesday against the poultry giant Perdue Farms and an Eastern Shore farm where Perdue chickens are raised, contending that the farm is polluting the Chesapeake Bay with manure-laden runoff.

The suit, filed by the Assateague Coastal Trust, says that water flowing off the farm near Berlin, Md., carries high levels of bacteria, as well as pollutants blamed for the Chesapeake's "dead zones." Environmentalists said they think the farm's owners store chicken manure in large outdoor piles near ditches, where it is likely to run off with the rain.

The farm "appears to be an out-of-control situation, when it comes to animal waste," said Kathy Phillips, an employee of the group.

The lawsuit is the latest sign of rising tensions about animal manure, both on the Eastern Shore -- where 568 million chickens were raised last year -- and across the country. In the 40 years since the first Earth Day, the United States has succeeded in regulating some pollutants that flowed out of factory pipes or sewage plants, but it has struggled with a growing amount of manure produced at supersize farms.

A Perdue spokesman declined to comment Tuesday, saying he could not speak about pending litigation. In December, the company defended the farm in a statement to the Baltimore Sun.

Alan and Kristin Hudson, the farmers named in the lawsuit, did not return a call to their home Tuesday.

The Maryland Department of the Environment has an open investigation into the Hudson farm. The agency has found high bacteria levels in ditches draining from the property, spokeswoman Dawn Stoltzfus said Tuesday. These eventually drain into the Pocomoke River, a Chesapeake tributary, Phillips said.

But Stoltzfus said the only pile of waste she was aware of on the property was not chicken manure but treated human sewage, shipped to the farm for use as fertilizer.

The lawsuit asks a Maryland District Court judge to assess fines of $37,500 for each day that the farm violated the federal Clean Water Act. Activists said they counted at least eight days in recent months when fines might be warranted. It also asks that the farm be forced to adopt new environmental practices and allow environmentalists to take water samples to check compliance.

"The notion of the family farm is long gone," said Scott Edwards, of the national Waterkeeper Alliance, another party to the suit. "These are factories. . . . They produce waste, they produce pollutants, they need to be regulated for environmental compliance."

In the Chesapeake, runoff from animal manure accounts for about one-quarter of the nitrogen and phosphorus pollution that feed "dead zones" downstream.

The bay's manure pollution has actually been reduced by about 20 percent over the past 25 years, federal data show. That is the result of intense efforts to cajole and pay farmers to make improvements on their properties, as well as voluntary changes at farms. But even this success is only half the progress achieved at sewage plants around the bay watershed.